In synthetic aperture radar (SAR) systems, a highly precise time reference is of considerable importance for exact measuring results. If several SAR systems are used, for example, on different satellites, a mutual balancing of the individual time references of the SAR systems is also important for a precise radar measurement.
European Patent Document EP 1 065 518 discloses a radar system which has a number of SAR systems on satellite- or missile-supported platforms. In order to avoid drift of the internal oscillators of the SAR systems, which are used as a time reference, a microwave or laser connection between the individual SAR systems is used to transmit an oscillator frequency from a main oscillator to the other oscillators, and thereby to synchronize these oscillators.
The essay “Oscillator Clock Drift Compensation in Bistatic Interferometric SAR”, M. Eineder, IGARSS 2003, Toulouse, IEEE Proceedings of IGARSS'03, describes the compensation of the drift of time references in SAR systems. The transmitters and receivers of the radar signal are spatially separated, and the oscillator frequency is exchanged between the receiving satellites via an inter-satellite connection in order to achieve a synchronization of the time references.
Drift compensation in such systems requires additional inter-satellite connections for transmission of the oscillator frequency. Moreover, additional measuring-relevant parameters cannot be determined by this method, and other compensation methods require additional components for implementing control mechanisms. However, the use of these control mechanisms requires time which is lost during the actual radar measurement. The scanning for the referencing thus remains limited to a few hertz.